[ConservativeStLouisGuy]

OOOPS! KMOX (1120 AM) is broadcast from St. Louis, Missouri....

[Eric in the Ozarks]

Those clear channel stations on AM are a hold-over from radio's early days. The FCC rules state that at local sundown, all stations on certain frequencies either reduce power or go off the air (called daytimers)to allow a dozen or so 50,000 watt US stations to cover huge areas. This originally was for nation defense.
Likewise, some AM stations broadcast directionally, like KXEL. Someone said they could pick up Waterloo, Iowa in Greenland some cloudy nights when the skip was just right. I believe there are Canadian clear channel stations, too. One is at 540 on AM.